Process for the manufacture of esters



Feb 14, 1939- J. F. HARRINGTON 2,147,341

PROCESS FOR THE MANUFACTURE OF ESTERS A Filed sept. .16.; 1930 3 Aaah?Fd ZM awww/tof,

Patented Feb. 14, 1939 UNITED lSTATES PATENT omcg A Y PnocEss Fon.'iliglzNuFAc'r-.Unn on Joseph F. Harrington, Highland1ark, ApplicationSeptember 16, 1930, Serial No. 482,306 22 cmins. "(ci.' 26o-48s) Thisinvention relates to the art of making esters by a process that may berun continuously and the following is a clear and exact description.

It has been known for some time that estersy 5 may be made by .mixingtogether an alcohol and aliphatic acid to be esteriiled, such as aceticacid, together with a large quantity of sulphuric acid as a catalyst andupon heating the esterialcohols and certain iso-alcohols there isconsiderable decomposition p rticularly with those alcohols of more thantw carbon atoms.

To prevent suchdecomposition it is necessary to have a processwhichcontrols the various factors aecting the reaction. It is thepurpose vof my invention to provide a methody whereby. either primary orsecondary alcohols may beesterliled with practically equal facility,producing very high yields of ester with practically no decomposition.Moreover the advantagof myinvention is that the process can be operatedcontinuously y2li although if desired I'the same process can be adaptedto a batch process. The success of my intention is based upon a correctcorrelation of the various factors entering into the esteric'atlon ofalcohols with aliphatic acids, which factors I nd'to be as follows:

l. Time of esterication.

2. Quantity of catalyst.

3. Concentration of catalyst. l 4. Law of mass action.

ySi. Amount of waterpresent-in the reaction mixture. l 6. Temperaturecontrol of distillation.

A11 of these factors 'are inter-related-one with 40 another and as theresult produced depends i hol and to feed continuously tothe reactionstill a supply of aliphatic acid and alcohol lnapproximately theoreticalproportions, and to remove simultaneously a proportionate quantity oiester, alcohol and water. in the distillate. ,It is ob- 56 vious thatunder such a process the time of contact of the alcohol-and aliphaticacid in the re4 action s tili .must be suiilcient to develop'the esterwhich is being continuously removed. t,

.Now it is well known that an alcohol aud aliphatic acid react veryslowly in the absenceof a 5 suitable.accelerator such as a highlyionized mineral acid or other material, which accelerator u may for thepurpose of designation be termed a catalyst. I have found that in theoperation of my'process an extremely small amount of cata- 10 lyst isentirely inadequateto promotegthe esteriilcationin the time periodvallowed under the conditions of operation. I have tried 'for examplesuch small percents of concentrated sulphuric -acld as .1% to .5% byvolume on the total charge 15I of esteriilcation components in -myprocess and the distillate produced is of very low ester value andentirely unsatisfactory from the standpoint of industrial operation.4

In `the production of primary or secondary 20 butyl acetate from aceticacid and the corresponding. alcohol, I have. found that a properconcentrationy of catalyzer depending on the strengthef acetic acid inthe reaction 4kettle is necessary to develop the desired desreeofesteri- 25 ication in the time period allowed, yet this concentrationmust notv exceed certain denite 1.1m-, its, `or decomposition due todehydration of the 'alcohol will result. For example, using acetic acidof '70% strength the quantity of sulphuric acid 30 should be a minimumof 1.7% and a maximum of 3% by volume 4oi the esterication components:for lacetic acid the quantity of sulphuric acid should be a minimum of1% and a maximum of 1.8% by volume of the esteriiication compo- 35nents; using 90% acetic acid, the quantity ofsulphuric acidV should be aminimum of .7% and a maximum of 1.5% by volume of the esterlflcationcomponents; the lower limit is required to produce ester concentrationof at least and the higher 40.

limit is necessary to prevent decomposition. Likewise in the case ofamyl acetate, primary or secondary, I have found that the strength oi'acetic acid a'nd concentration of sulphuric acid 'to'be'requiredcorresponding to the above for the 45 butyl acetates and with thesameapproximate limits. In the case of isopropyl acetate. I'have' foundthere is less tendencyto decomposition at or near the above statedhigher limits and these may therefore be somewhat exceeded. The lower.50 I

limit is required in order to produce an ester of at least 85%, -andwith isopropyl acetate I .prefer to operate at about the mean of theupper and lower limits. A

Itis evident that .the percent of sulphuric acid 55 .by a method thatwill be disclosed later.

I have also found that in place of using highly ionized mineral acids Ican also use corresponding percents by weight of certain salts such as.sodium bisulphate, potassium bisulphate, sodiumv or potassium acidphosphate and similar salts.

It is evident therefore that to develop the required esteriiication inthe time period allowed, it is necessary to use a large quantity ofcatalyst. On the other hand such alarge quantity of catalyst wouldordinarily promote dehydration and decomposition, especially in the caseof secondary alcohols if means were not found for controlling thestrength or concentration of such catalyst. This -is accomplished bymaintaining at all times in the reaction still a large volume of water.VThe water destroys the dehydration enect that would otherwise take placedue to the strong mineral acid' or other catalyst. 'I'he amount of watermaintained depends upon the particular alcohol and the percent ofcatalyzer. In general with I higher alcohols such as butyl .or amylalcohol,

,either removing water Vfrom the system as with primary or secondary,.I'prefer to maintain from 10 to 40% of water by vvolume in the reactionstill in respect to the total volume of materials in the reaction still.Preferably the water content will be about lli-25%. With isopropylalcohol which is less subject to decomposition as compared to the higheralcohols, I find it preferable to maintainfrom ten to thirty percent oi'water present, operating usually with about l5-25% but using a-higherconcentration of catalyzer. i

The presence of such a large amount of water would ordinarily impair theesterication process. The effect of this water however isvoiiset in an.-

other way -by taking advantage o! the law of.

mass action. A small volume of alcohol in contact with a large volume oialiphatic acid will esterify the alcohol to a very large degree. Thesame is true vice versa as a small volume of aliphatic acid in contactwith a large volume oi l vof eight to ten volumes of aliphatic acid inrespect to the volume of alcohol does not need to be strictly maintainedas I nd the processl works with a ratio of upwards of about live to one,but I prefer to operate at the ratio of eight'or ten to one.

In order to control the amount of water presentlin the reaction still Iprovide a means4 in the reflux line between the condenser and thefractlonating column to withdraw the water from the ester, alcohol andwater mixture in the distillate,

lower esters or removing a part of the wate and feeding another part ofthe water back to the reaction still in the case of higher esters, whichseparate a very large proportion of water. In either case I somanipulate the water regula# tion as to maintain the water in thereaction still at an approximately constant value, namely as set forthabove. f

By means of the reflux line, feeding back part of the distillate to thetop of the fractionating column in the usual manner of distillationprocesses, the temperature of distillation must be maintained underdefinite control. Under correct temperature control the distillate maybe brought over as a mixture of ester, alcohol and water, the esterbeing of a higherpercent and with eflicient fractionation practicallyneutral.

The required temperature control changes with small amounts of aliphaticacid, depending on the eiiiciency of the fractionating equipment. Thedistillate is neutralized lwith a solution of caustic soda or soda ash,dried over calcium chloride if desired and redistilled in the usualmanner in a finishing still. The first portions of distillate from theiinishing still run wet. but after dryness is Vobtained the material iscut to a tank for finished material. The water from the neutralizingtanks and calcium chloride tanks and water separated from the wateroperating still carry some entrained alcohol and ester and these waterscan be distilled to recover the alcohol and ester separately. l

Having described the general process I will give an illustration of themethod of operation with secondary butyl alcohol. I put in the reactionstill, say ten volumes of acetic acid of about 75% `strengthy to this Iadd one to one and one-half volumes of secondary butyl alcohol and about1.5% of concentrated sulphuric acid by volume on the total charge ofesterication components. I then heat to boiling for about a half hourand then start distillation, when distillation commences, I again beginto feed to the reaction still secondary butyl alcohol and 7,5% aceticacid, in

molecular proportions or in quantities corre-` sponding to the amount ofester and alcohol and water which is being removed in the distillate.For. each pounds of. secondary butyl alcohol added there is required81.5 pounds of '75% acetic acid and 19.5 pounds water are produced fromreaction in making 144.4 pounds 'of 85% ester. The total waterincluding'the water added with the acetic acid is 40 pounds'andapproximately this amount must be removed by the water sepa-v rator, foreach 100 pounds of alcohol added. The reiiux is adjusted so that thetemperature is controlled at .about 83 C. to 86 C., at the top of thecolumn, and water is removed from the water separator at a rate thatmaintains at all times the quantity of water in the-reaction kettleapproximately constant as corresponding tothe condition that exists atthe beginning of the run. By this means the operation vmay be' continuedday after day and all factors enumerated above are brought intopropercorrelation.

hol, an eiliciency of 97.5%.

Using this method oi' operation I have been able to produce esters of4an exceptional degree of purity atleast equal to 'or above the usualcommercial 85%, and with only the two distillations of generating andfinishing. Moreover due to a scientific control I have been able tooperate at a very high degree of efilciency with only slight losses duetodistillation and practically none due t decomposition. For exampleusing 75% acetic acid and secondary butyl alcohol the theoretical yieldshould be 144.4 pounds secondary butyl acetate of 85% ester for each 100pounds of alcohol. I have been able to obtain 140 pounds of 85% esterfrom each 100 pounds of alcohol or an eiliciency of 97%. This could besomewhat increased by recovery of uncondensed vapor during distillation.Likewise using 75% acetic acid and commercial 88% isopropyl alcohol thetheo.- ietical yield should be 135.3 pounds of 85% ester for each 100pounds of isopropyl alcohol. I have been able to.obtain 132 pounds of85% isopropyl acetatel from each 100 pounds of isopropyl alcowise wouldbe improved by recovery of uncondensed vapor during distillation. Inboth cases the eihciency, `based on'the acetic acid used corresponded tothe efiiciency based on the alcohol.

As a further illustration of the method o f operation with-isopropylalcohol I put into the reaction still say ten volumes of acetic acid ofabout 75% strength, to this I add one and one-half volumes of commercial88% isopropyl alcohol and about 2% of concentrated sulphuric acid byvolume on the` total charge of esteriflcation components. I then heattoboiling for abouta half. hour and then start distillation. whendistillation commences Ibegin feeding to the reaction still isopropylalcohol a'nd75% acetic acid in molecularproportions and in quantitiescorresponding to the amount of ester, alcohol and water which is beingremoved in the distillate. For each 100 lpounds of commercial -88%isopropyl alcohol there is required 90.2 pounds of 75% acetic acid. and20.3 pounds of water are produced from' re-I action in making 135.3pounds of 85% isopropyl acetate. The total water including the wateradded with the acetic acid and alcohol is54.7 pounds, and approximatelythis amount must be removed by the water separator for each 1,00

pounds of 88% isopropyl alcohol added.

As a further illustration o! the method' operation with secondary or.primary amyl alcohol or with these in combination, I put into thereaction still say ten volumes of acetic acid of about 75% strength, andto this I add one and one-half volumes of amyl alcohol and about 1.5% ofconcentrated sulphuric acid by volume on the total charge ofesterication components. I then heatto boiling for about one-half hourandv then start distillation. When distillation commences'I beginfeeding to the reaction still amyl alcohol and 75% acetic acid inmolecular proportions and in quantities corresponding to the amount. o'fester and alcohol and waterwhich is being removed in over more than 34pounds of water in eachi 130.2

This eiilciency likepounds of ester, and in order to control thestrength of acetic acid in the reaction kettle constant, part of thewater from the water separator must be fed back vto the reaction kettle.

In order to explain the operation f the equipment necessary a drawing isshomi in Figure I, of the design of the esterification equipment(including the primary distillation equipment, with its' accessories).

A is the reaction kettle, B Ais 'a fractionatlrig column, C is thecondenser, D is the water separator, E is the neutralizing tanks, F isthe alcohol feed tanks, G is the acid feed tank, H is a receiver forWater separated and I is the valve lcontrol on the alcohol feed tank. 2is the valve control on theacid feed tank,"3 is'a flow meter on`thealcohol feed, 4 is a flow meter on the acid feed, 5 is a flow meter onthe condensate line to the vneutralizing tanks, 8 is a flow meter on thereflux return line to thefractionating column, I is the reflux returncontrol valve, 8 isv a vent pipe, 9 is a recording thermometer on thefractionating column top, I 0 is the control valve on water removed fromthe water separator, I I is the control valve on return of water to thereaction kettle, I2 is a flow meter forthe water separator, i3 is thesteam coil in the reaction still and I4 is a flow meter on return waterline to reaction still.

The alchohol and acetic acid are `supplied to the reaction still fromtanks'lll and G respectively through the ow meters 3 and 4 respectively.The steam is turned lon throughathe steam coil I3. When distillationbegins the vapors pass up the fractionating column B and are condensedin condenser-(3. 'I'he condensate flows to the water separator and thewater separates into a bottom layer. The top or ester layer is partiallyfed back to the top pf`the fraetionating column to maintain propertemperature control by means of the reflux return control 1, through theflow meter 6. The balance of the condensate ows through the flow meter 5to the neutralizing vtank E. The water is removed by means of controlvvalve I8, through ow meter I2 into tank H, or is partly returned to thereaction still through control valve II when necessary.

My process is of general application and it will readily be apparent toone skilled in the art that methyl, ethyl, propyl and butyl esters ofaliphatic acids may be Lprepared\\by a method4 entirely analogous tothose described above. With re- 'gard to the preparation of esters ofhydroxy aliphatic acids -and dicarboxylic acids, it is pointed out thatin the finishing or purication of these last named esters it isadvisable to work in vacuum.

As'usedin the claims, mineral acids refer to sulphuric, hydrochloric,nitric and 4phosphoric acids.

As an additional step in the process use may be made of series stillsand columns so that the distillate from the reaction still is fedcontinuously to this additional equipment for continuous finishing.

In the above specification, I- have (given, as anexample, the use ofilve to ten volumes of the aliphatic acid, to one volume of the alcohol.

These figures, of course, are illustrative and not' limiting. Ratios ofthe order of 5:1 to 10:1 will hereinafter be included in the expression,"a

moderate excess" of the acid.`

Having thus described my invention, what I claim as new and desiretoprotect by Letters Patent is:

l. Acontinuousmethodior producing esters which comprises reacting amoderate excess of a mono-carboxylic aliphatic acid with a mono hydricalcohol in the presence of a small amount of a catalyst selected fromthe group consisting of mineral acids and acid'salts the ratio of saidaliphatic acid to alcohol being not substantially over 10:1, thereaction mixture also containing about 10 to 40% by volume of water, andthereafter removing from the reaction zone by distillation a productcontaining ester, alcohol and water, and feeding said aliphatic acid andsaid alcohol and water to said still, in such proportions as to replacethe distillate as removed.

2. A continuous process for producing esters which comprises reacting amoderate excess of a mono-carboxylic aliphatic acid with a monohydricaliphatic alcohol in the presence of a small amount of catalyst selectedfrom the` group consisting of mineral acids and acid salts, the reactionmixture also containing'about 10 to 40% by volume of Water during theentire period of reaction, andthereafter removing from the reaction zoneby distillation a raw distillate suiilciently rich in ester content, sothat after separating water by stratiiication and neutralization, and asingle subsequent distillation, a product is obtained which contains atleast 85% ester.

3. A continuous method for producing esters which comprises reacting amoderate excess of a mono-carboxylic aliphatic acid with a monohydricalcohol in the presence of a small amount of a catalyst containing amineral acid radical, the reaction mixture also containing asubstantially constant large amount of water, and thereafter removingfrom the reaction zone by disw tillation, a product containing ester,alcohol and water.

4. A process of making esters which comprises reacting a moderate excessof an aliphatic monocarboxylic acid with an aliphatic-monohydric alcoholin the presence of at least about 10% by volume of water, and in thepresence of av catalyst selected from the group consisting of mineralacids and acid-salts, until the resultingcompositlon approximatesequilibrium, distilling oi a distillate containing a high ester contentand continuously feeding intogthe still a feed mixture of said acid,alcohol and water corresponding approximately in composition-to thedistillate withdrawn from the system.

5. A continuous process of preparing esters comprising reacting five toten volumes of an aliphatic carboxylic acid with one volume of analiphatic alcohol in the presence of a small amount of a catalystselected from the group consisting of mineral acids andacidsalts,'continu ously adding the said acid and alcohol to the reactionmass in amounts about equal to theoretically reacting proportions,maintaining a large amount of water at a constant value in th'e reactionmass, by continuously removing the water formed 4by the ester-iiicationreaction Aand continuously removing'the ester'iormed.

6. A continuous process of preparing 'esters comprising reacting ve toten volumes oi an aliphatic carboxylic acid with one volume of anvaliphatic alcoholI in the presence of .7% to 3% by volume sulphuric acidcalculated on the total amount of reaction mass. continuouslyadding the'said aliphatic carboxylic acid and alcohol to the reaction mass inamounts'about equal to theoretically reacting proportions,maintaining-,a constant amount of water in the reaction masscontinuously removing the water formed by the amasar isopropyl alcoholis reacted with acetic acid to l form isopropyl acetate.

10. A process as set forth in claim Z in which a propyl alcohol isreacted with acetic acid to from a propyl acetate. i

11. A process as set forth in claim 1 in which secondary amyl alcohol isreacted with acetic acid and to form secondary amyl acetate:

i2. A process asset forth in claim si in which an amyl alcohol isreacted with acetic acid to form amyl acetate.

13. A continuous process of preparing esters comprising reacting five toten volumes of an aliphatic carboxylic acid with one volume of asecondary aliphatic alcohol in the presence of 0.7% to 3% by volumesulphuric acid calculated on the total amount of reaction mass,continuously adding the said acid and alcohol to the reaction mass inamounts equal to about theoretically reacting proportions, maintaining aconstant amount of water in the reaction nf'iass equal to from 10 to 40%of the total volume, maintaining the acid and alcohol in contact witheach other for a sumcient period of time to eiect a degree ofesterication equal at least ence of a catalyst in sumcient concentrationto y obtain a high degree of esteriication, said catalyst being selectedfrom the group of mineral -acids and acid salts, said catalyst beingpresent in an amount which is inversely proportional to the strength ofsaid aliphatic carboxylic acid, continuously adding the said aliphaticcarboxylic acid and said alcohol to the reaction mass in amounts aboutequal to theoretically reacting proportions, maintaining a large andsubstantially 'constant amount of water in the reaction mass andcontinuously removing the ester formed.

15. A continuous process oi prepa esters comprising reacting ve to tenvolumes of an aliphatic carboxylic acid with one volume of an aliphaticalcohol in the presence of .7% to 3% by volume of sulphuric acidcalculated on the total amount of reaction mass and being present in anamount which is inversely proportional to the strength of said aliphaticcarboxylic acid, continuously adding the said al1- phatic carboxylicacid and said alcohol to the reaction mass in amounts about equal totheoretically reacting proportions, maintaining a coristant volume o!water in the reaction mass equal t'o 10% to 40% of the total mass byvolume, and

maintaining tl'ie aliphatic carboxylic acid and alcohol in contact witheach other for sumcient' time topromote at least %'esterication.

16. A process of making esters which comprises reacting an excess of analiphatic monocarboxylic acid 'with an aliphatic monohydric alcoholPatent llo'.

2,147,841 ,and' water until the resulting composition ap-v proximatesthe equilibrium composition, distilling oi a distillate containing ahigher ester content than that occurring in the corresponding ternaryester content than the correspondingaseotrope,

cEarIFIcATE or coRREcTIoN;

distilling and continuously removing the formed.

20. A continuous process for producing esters whichl comprises reactingabout six volumes of azeotrope and continuously feeding into the stillacetic acid with one volume of secondary butyl 5 a feed mixture of saidacid, alcohol and water alcohol in the presence of a small amount ofcorresponding in composition. to the distillatey sulfuric acid as thecatalyst for a time suilicient l withdrawn from the system. toproduce areaction mixture which approxl- 17. A continuous process for preparingesters mates equilibrium conditions, then continuously comprisingreacting aboutsix volumes of a lower feeding in a mixture to saidreaction. mix- 10 aliphatic. carboxylic acid-with one volume of a turecomprising substantially stoichiometrical lower aliphatic monohydricalcohol for suillcient amounts of Yacetic acid and secondary butylaltime an'd in the presence of a strong mineralI cohol, distillingandcontinuouslyremoving the acid catalyst in sufilcient concentration toobtain "ester formed. a highidegree of esteriflcation, continuously add-2,1. A prOceSS fOr making eSiSiIS -0f aliphatic l5 ing the saidaliphatic carboxylic -acid and said secondary monohydric'alcoholscomprising formalcoholto -the reaction mass in. amounts about ins a`reactiOnmiXtUIe 0f Ve 1D0-ten Volumes equal to theoretically reactingproportions .toof dilute aliphatic monocarboxylic acid to one getherwith water, distilling, fractionating the' volume of. alcohol,distillingIsaid reaction mixdistillate and continuously removing the ester' turein the presence of 1% to 3% of sulfuric 20 .formed by condensation and'stratiilcatiom acid, continuously adding a mixture ofsaid dilute l18. Acontinuous process for preparing esters organicv acid and alcohol insubstantially equi;- y comprising reacting'about six-volumes of a lowermolecular portions, fractionating the distillate fatty acid witli'onevolume of a lower aliphatic'` and condensing andstratifying whereby anester 'secondary alcohol in the presence of a smallv fraction of greaterthan 80% ester content is amount 'of sulfuric acid until the resultingcomseparated. l r position approximates .equilibrium conditions. 22. Aprocess of making esters of aliphatic seccontinuously adding-a mixturecomprising said ondary monohydric alcohols comprisingjforming fattyacid, said alcohol and water, ldistilling and a reaction mixture ofbetween about 5 to about continuously removing the ester formed. 1 10volumes of acetic acidcontaining from v10% 3o 19.- A continuous processfor producing esters to 20% water to one volume of secondary butyl whichcomprises reacting-about six volumes' of alcohol, distilling saidreaction mixture in .the acetic acidwith one volume of a loweraliphatic. presence of 1% to 3% of a highly ionizable inin-` secondary.alcohol inthepresence of a catalyticv eral acid, fractionating thedistillate,. distilling amount of sulfuric acid until the resultingcomand removing the ester formed, and continuously4 positionapproximates equilibrium conditions, adding a mixture of said aceticacid .and alcohol continuously adding acetic acid and said alcoholl tosaid lreaction mixture to .compensatefor th in about theoreticallyreacting-proportionsand ester and w'ater withdrawn/watersuillcient'togiveadistillatehavingahigher 1 JOSEPH E'HARRINGTON. n

, f- Februar-11 19595 l .IOS-LEPHJF. HARRINGTON.. A l l lisherebycertifiedthat error appearsinthe abovenumbered patent requiringcorrection as fo1lovvs In tl1e drawing,fo-r the legendllilcohol -Feed.vTankf designating tankli reed Still.; and for the legend "Reaction'catae 1yst" designating .tanlr F .read i\ l l.c: ho 1A lFeed Tenir;andthe'ttlate said Letters. .Patent should bev read with thig.correction' therein thatthe samemay oonform tothe record of the case inthetllatent lOlfric'e. signed and sealed this litiriifaly of April, A.D. 1,959.'

Acting' Commissioner of'. Patents.

